This article's content is accurate to the most recent public game version, 0.4.8d.
"Projects horrifying images directly into an enemy's mind. Deals Mental damage, 50% chance for Stunned."
Cost: 6 MP
Source: Equipping the Illusion Core.
Terrifying Visions is a spell that deals slightly below average 
Mental damage with a 50% chance to inflict the 
Stunned status effect to a single enemy target.
While expensive for the damage output it provides, knocking an enemy out of combat even temporarily can be tremendously useful.
The following enemies can cast Terrifying Visions: